Transformers may be widely used for low, medium and high voltage applications.
It is widely known that the transformers may suffer from temperature raises during operation. These temperature issues have to be avoided or even reduced as low as possible in order to achieve a better performance and a long life.
A particular type of transformers is a dry-type transformer which may use a gas such as air to refrigerate for instance the winding or coils thereof. This air cooling may be forced or natural. In case of forced-air cooling the blowing equipment may be positioned to blow the airflow to the winding.
It is also known the use of electric shielding devices for protecting the clamping structure of the transformer from electric fields generated by the winding. An example of such an electric shielding device is disclosed in EP2430643B1. The transformer comprises windings and clamps linked to yokes for supporting the whole transformer. The electric shielding arrangement is arranged between the clamp and the winding.
For dry-type transformers with air-forced (AF) refrigeration, the protective sheet or electric shielding device which covers the clamps of the transformer may block the airflow that is directed to the winding, particularly to an inner zone of the winding arrangement. This inner zone of the winding may correspond for instance to a lower level voltage portion of the transformer and the outer zone may correspond for instance to a higher level voltage portion of the transformer. Depending on the case the outer zone may receive the cooling airflow barely without obstacle despite of the shielding device. However, the inner zone which is surrounded by the outer zone and the shielding device may not receive an adequate flow rate for keeping the temperatures at a desired level.
It has now been found that it is possible to provide an improved cooling arrangement for dry-type transformers provided with electric shielding devices, which allows to properly refrigerate the winding and may be more efficient than known solutions.